Continuous method for electropolishing nickel and nickel-containing alloys



May 4, 1948.

C. L. FAUST ET AL CONTINUOUS METHO 2,440,715 D FOR ELEcTRoPoLIsHING NICKEL AND NICKEL-CONTAINING ALLoYs Filed July 23, 1943 4 Sheets-Sheet 1 Ef-i Iooesmso4 May 4, 1948.

c. l.. FAUST ET 2,440,715 CONTINUOUS METHOD FOR ELEC POLISH G NICKEL AND NICKEL-C Al'NING ALLO Filed July 1945 4 Sheets-Sheet 2 WOM Cene/ Es 5067: En. 0. /V/ue.

May 4, 194s. c.

FAUsT ET AL 2,440,715 TI U ETHOD FOR ELECTROPOLISHING CK A NICKEL-C AINING ALLOYS Filed July 1945 4 Sheets-Sheet 3 lo 9o May 4, 1948.

c. FAUsT ET 2,440,715 CONTINUOUS METHOD FOR ELECT OLISHING NICKEL NICKEL-CONTAINING ALLOYS iled July 23, 1943 4 Sheets-Sheet 4 Z, H2O

ZHYE'z-QF 5 Patented May 4, 1948 CONTINUOUS METHOD FOR ELECTRO- POLISHING NICKEL AND NICKEL- CONTAINING ALLOYS Charles L. Faust and Paul D.

Ohio, assixnors.

Miller, Columbus,

by mesne assignments, to Battelle Development Corporation,

Columbus,

Ohio, a corporation o! Delaware Application July 23, 1943, Serial No. 495,842

6 Claims. (Cl. 20d-140) This invention relates to an improved electrolytic bath for anodically polishing nickel and nickel-containing alloys. More particularly, the invention pertains to a method of continuously electropolishing nickel by means of an electrolyte from which excess nickel dissolved during the electropolishing step is continuously plated out on the cathode as metallic nickel.

Nickel and its alloysthat are rich in nickel may be anodically polished in an electrolyte containing, as an essential active ingredient, sulfuric acid or a mixture of sulfuric and phosphoric acids. The concentration of the sulfuric acid, when used alone, as well as the combined concentration of the mixed sulfuric and phosphoric acids should be at least 50% by weight of the solution and preferably not more than 95% by weight of the solution, the balance being largely water. For practical purposes, about 90% is the upper limit for the total acid concentration. While it is possible to produce good polishes with aqueous mix tures of sulfuric and phosphoric acids containing as much as 50% water, it has been found preferable to keep the water content of the bath relatively low, since, in general, baths containing lower proportions of water may be operated 'at lower current densities and, therefore, at a lower cost, to give satisfactory polishes. The relative proportions of the essential acids may vary between rather wide limits, as, for instance, from about 3 to about 76% of sulfuric acid and from 0 to about 78% of phosphoric acid, the total acid concentration being more than 50%.

Unless otherwise specified, all percentages referred to herein will be understood to represent percentages by weight rather than by volume. Also, references to acids should be understood to refer to the formula weights as H2804 and Hal-"04. Where phosphoric acid is referred to, orthophosphoric acid is meant, since that is the stable form under the temperature conditions obtaining in the operation. However, phosphoric acid may be added in some other form, such as pyro phosphoric acid or meta-phosphoric acid.

Thus, a mirror-like ilnish .hay be produced by anodically polishing nickel in aqueous solutions containing 15% H2SO4 and 63% H3PO4, using a current density of amperes per square foot and a bath temperature of 115 to 130 F. The time required to produce the polish is determined by the original physical character of the nickel being polished. However, during electropolishing under these conditions, a nickel compound is formed which breaks up at higher temperatures to form nickel sulfate. Consequently, a used bath precipitates nickel sulfate on the hot surfaces of the heating coils and the cathodes. As a result, the tank voltage increases because of the incrustation on the cathodes, and temperature control is impaired by the precipitation of the nickel salt on the coils during the warming up period. Therefore, in order to maintain continuous operation it is necessary to remove dissolved nickel from the bath.

The aforementioned difficulties can be temporarily overcome by reconditioning the bath. Reconditioning consists of heating at high temperature to precipitate nickel sulfate, l'tering, adjusting the bath composition, and cleaning the cathodes. The bath can then be operated until reconditioning again becomes necessary. Since such reconditioning is not commercially feasible in the production tank, separate tanks and the attendant auxiliary equipment are needed. Thus, reconditioning adds to the operating cost.

Commercial operation can be greatly improved by having a bath which operates continuously without need for batch reconditioning, without impractical changes in composition, and without increase in operating voltage. In any case, continuous operation requires that nickel be removed from the bath.

If the aforementioned bath, containing 15% H2SO4 and 63% HaPOi, is operated at a temperature high enough to precipitate nickel sulfate continuously, for instance, at F., then a current density of more than 250 amperes per square foot must be employed, as otherwise the nickel surface, although given a brilliant finish, will be pitted.

rent densities of 125 to 250 amperes per square foot. This process has been described in `a copending application of one of us, Charles L. Faust, S. N. 440,338, filed April 24, 1942, now Patent No. 2,429,676.

However, while the last mentioned bath is capable of fairly continuous operation, periodic ltration is necessary to remove the continuously precipitated nickel sulfate. Furthermore, the nickel is recoverable only in the form of a salt. The use of high temperatures is also objectionable because it increases the cost of operation.

It is therefore an important object of the present invention to provide an electrolytey and a method for electropolishing nickel and valloys rich in nickel that is capable of continuous operation at low current densities without need for bath reconditioning, `without involving any objectionable amount of precipitation of nickel salts, and without impractical changes in composition.

Another object of this invention is to provide an electrolyte and a method for electropolishing nickel capable of being operated continuously without a progressive rise in operating voltages.

A further object of this invention is to provide an electrolyte and a. method for electropolishing nickel capable of continuous operation at low temperatures.

Still a further object of this invention is to provide an electrolyte and a method for electropolishing nickel by the use of which excess nickel dissolved from the anode in the electropolishing step is continuously plated out as metallic nickel on the cathode of a degree of purity and in a physical state suitable for recovery and use as nickel.

Other and further objects and features of the present invention will become apparent from the following description and appended claims,

In the accompanying drawings, which show ternary systems of sulfuric acid (H2804), orthophosphoric acid (HaPOO and water (H2O) in percentages by weight: l

Figure 1 illustrates areas representing bath compositions which, by the addition of between 0.04 and 2.5% of hydrochloric acid (HC1), are operative at temperatures between 80 and 140 F. for effecting the electropolishing of nickel and nickel alloys with simultaneous plating out of excess dissolved nickel.

Figure 2 illustrates areas representing bath compositions which, by the addition of between 0.3 and 1.0% of hydrochloric acid (HC1), are operative at a temperature of 115 F. for effecting the electropolishing of nickel and nickel alloys with simultaneous plating out of excess dissolved nickel.

Figure 3 is similar to Figure 2 except that it represents bath compositions operative at 90 F.

Figure 4 is similar to Figures 2 and 3, except it represents bath compositions operative at 135 F.

We have found that the addition of hydromixed sulfuric acid-phosphoric acid baths within the general limits delineated in Figure l yields baths in which nickel or nickel-containing alloys can be polished to a bright, mirror-like, pitfree finish at temperatures in the general range of from 80" to 140 F. and at current densities from 50 to 300 amperes per square foot. We have further found that under these conditions the excess of nickel dissolved from the anode can be continuously electrodeposited as metallic nickel on the cathode. Thus, although hydrochloric acid is not essential for the production of a. brilliant mirror-like electropolish in a bath containing sulfuric and phosphoric acids, the addition of minor percentages of hydrochloric acid does serve to make possible continuous operation without appreciable precipitation of nickel salts, change in viscosity, or increase in tank voltage.

Whereas the copending application, S. N. 440,338 of Charles L. Faust, relating to the electropolishing of nickel shows that electropolishing cannot be carried out so effectively in phosphoric acid baths containing no sulfuric acid, the present invention now makes this entirely practicable. Heretofore, the phosphoric acid baths, containing no sulfuric acid, electropolished nickel for a short period of time when they were fresh. However, the baths rapidly became very viscous, so that tank voltages and drag-out were high, polishing results were poor and the useful period was very short. The high viscosity apparently resulted from the fact that nickel is very soluble in straight phosphoric acid.

By virtue of the present invention, the phosphoric acid can be maintained in practically its original electropolishing condition because the nickel deposits out on the cathode during the operation of electropolishing. Thus, there is no build up in nickel concentration to render the bath viscous and of a short useful life. The straight phosphoric acid bath, however, does not have so good throwing power as the H2SO4- HaPOi combination. Therefore, the phosphoric acid bath is included only in the broad range of operable bath compositions.

In the case of baths containing more than about 45% of sulfuric acid, although hydrochloric acid additions according to the teaching of this invention tend to cause deposition of metallic nickel from solution, the solubility of nickel sulphate is so low that no significant, practical improvement results,

The effectiveness of the hydrochloric acid results from the chloride that it introduces into the bath. Consequently, any medium for introducing-chloride additions can be used in place of the hydrochloric acid or in conjunction with it, We can, therefore, accomplish our improved results by introducing a soluble metal chloride such as the chloride of sodium, potassium, calcium, magnesium, nickel, aluminum, chromium, and the like.

The manner of introducing the chloride apparently is immaterial, but the simplest and most expedient method is to use hydrochloric acid. If a metal chloride were to be used, the quantity would be selected on the basis of equivalency to the chloride content of HCl specified in the opchloric acid to straight "phosphoric acid and to erative ranges that are disclosed herein. Since the specified purpose of this invention is to remove metals from the electropolishing bath, it is preferred to use hydrochloric acid, for the metal chlorides introduce a metal into the bath. We have also found that the desired effect of chloride additions can be achieved by introducing small concentrations of chlorinated organic acids, such as monochloroacetic acid,

The electropolishing bath as freshly made up with an addition of a chloroacetic acid gives no 6 tained. In running these tests, the HC1 was maintained at the proper value by periodicadditions of concentrated hydrochloric acid. The amount to be added was determined by chemical chemical test for a chloride. However, after a 5 analysis for chloride in the bath. short period oi' use for electropolishing, the bath While HCl additions tend to facilitate the platgives a positive test for chloride. It is, therefore, ing out of nickel in all H2SO4H3PO4 baths, the apparent-that the chloroacetic acid eiectively inemciency of nickel deposition at the cathode and troduces chloride into the bath to accomplish the continued operation without precipita-tion probresults of this invention. lems depend upon the H2SO4/H3PO4 ratio and the The equilibrium condition of good operation is water content. In order for the deposition rate to maintained simply by replacing water, HC1 and equal the anodic -dissolution rate, a certain minidrag-out losses. The cathode nickel, plated out mum concentration of dissolved nickel apparently during the electropolishing operation, consists of is required. The amount of nickel in solution dedense metal havingapurity in excess of 98% and 15 pends upon the HzSO4/H3PO4 ratio and the generally as high as 99.6%. Such a material water content, which also determines the soluis particularly well suited for use as anodes in bility limit If the minimum concentration of nickel electroplating tanks. nickel for a suitable deposition rate is greater Only minor percentages of chlorides are rethan the solubility limit, precipitation will be quired to produce the desired effect. There is 2o unavoidable. no practical way to add chloride ions, per se We .have found that upon addition of HCl withto the bath, or to determine what is the necesin the disclosed range, certain bath compositions sary chloride ion concentration. We have deare operable in continuous electropolishing withtermined that an adequate chloride ion concenout objectionable precipitation of nickel salts. tration results when a certain percentage of a These bath compositions are illustrated on the chloride is present in the bath. For simplicity in triaxial diagrams of the accompanying drawings. maintenance and in expression of analysis, the On the diagram of Figure 1 are represented two chloride content is calculated as HC1. As shown areas, a larger area delineated by the solid straight by the data in Table I, satisfactory operation is lines joining the points A, C, D, E, F, G, H and obtained when the HCl concentration is but A, and a wholly enclosed smaller area delineated slightly in excess of 0.04%. These tests were made by the dotted straight lines joining the points B, by adding HC1 to a standard 15% H2SO463% I, J,K,G, L,Mand B.

l) TABLE I Per cent nickel plated at cathode for various HCl 1 Additions to the 15% H2SO4-63% HaP04-22% H2O bath, for electropolishing nickel Parr at 000.0/ at .ma ..1 3 f E (l n (y n Dissolved HclJ Hol Hoi HC1 H0371 (1)131 113100371 Llasci from Anodc 2.0 e0 s2 50 75 ce 3.0 42 s4 94 se 4.0 00 95 90 4.5 42 9c 5.0 s4 91 6.0 c3 9s 101 7.0 00 a0 71 100 10s 9.0 ppm 102 102 12.0 Very slight ppt 95 No ppt. 34.0 99

No ppt.

1 Values based on amount ol' nicke 2 Based on weight of the bath.

l dissolved from thc anode for the interval of electrr-polishing shown.

3 Ppi. indicates formation of precipitate of nickel salt.

H3PO422% H2O electropolishing bath. Similar data for a H2SO4-38% H3PO427% H2O bath are shown in Table II. The criterion for satisfactory bath operation is the eicient plating of nickel at the cathodes and the absence of an objectionable precipitate of nickel salts.

These data indicate that satisfactory results are obtained when HC1 is present in amounts ranging from 0.04% to 2.5%. However, the lower range of from 0.04 to 0.4% is preferred because of the ease of maintenance and the absence of pitting tendencies on the work being electropolished.

Table I shows some fluctuation in per cent nickel plated out in baths containing 0.04% or more HC1. This small variation is considered to be caused by changes in water and HC1 concentration. Periods of operation below 100% deposition are oiset by periods of more than 100% so that no operational difliculties are encountered when water and HC1 contents are suitably main- TABLE II Per cent nickel plated at the cathode 1 For various HCl additions to the 35 H2SO438% H3PO427% H2O bath for electropolz'shing nickel l Values based on amount of nickel dissolved from the anode for the interval of electro olishing shown.

i Based on weig t of the bath. I Ppt. indicates formation of a precipitate of nickel salt.

The larger area defined by the lines AC, CD, DE, EF, FG, GH and HA represents bath compositions as regards percentages of HsPOi, or of HaPOi and H2804, which, when containing minor additions of HC1, are suitable for el-ectropolishing nickel and nickel alloys at some or all temperatures within the broad temperature range of from 80 to 140 F. Within part or all of this temperature range. baths of a composition falling within the designated area and containing chloride additions within the limits above given, are operative to impart a. bright polish to nickel and its alloys, while at the same time most of the dissolved nickel coming out of solution' plates out at the cathode to permit continuous operation with only a slight precipitation of nickel salts, if any.

The values for percentages of HsP04, H2804 and H20 at the points indicated on the boundary for this larger area are as follows:

HsPOl B :S04 H2O In general, therefore', the broad operative range lies between 21 and 85% H3P04, 0 and 45% H2804, and 15 and 34% H2O. The total acid concentration within this broad operative range has a minimum value of 66% and a maximum value of 85%.

It will be understood, of' course, that the operative range of bath compositions for satisfactory electropolishing of nickel and its alloys is even broader than that represented by the larger area just defined, but upon continued operation of baths whose compositions li outside of this larger area on the accompanying ternary diagram, there will be objectionable precipitation of nickel sulfate or else inefficient plating out of nickel, or both. Even within said larger area, some slight precipitation of nickel sulfate may occur for par ticular bath compositions at certain temperatures between 80 and 140 F., but such amount of precipitation will not, in general, be objectionable.

The wholly enclosed smaller area, lying within the straight dotted lines BI, IJ, JK, KG (full line), GL, LM and MB, represents the preferred ranges of bath compositions within which practically no precipitation of nickel sulfate occurs when the chloride content is within the limits given above and a proper temperature, within the range of from 90 to 125 F., is used for the composition selected. Under the conditions named, nickel and its alloys can be satisfactorily polished anodically, while, at the same time, dissolved nickel is plated out at the cathode at a rate suiiicient to maintain the dissolved nickel content below its saturation point, and thus prevent any substantial precipitation of nickel salts.

The values for the percentages of HsP04. H2804 and H2O at the points indicating the boundaries of this smaller area are as follows:

Point HsPO B180. H30

75 l0 l5 62 20 18 45 28 27 38 28 v 34 56 10 34 73 2 25 77 3 20 In this preferred operating area, therefore, the percentages of HaPOi lie between the limits of 38% and 77%, of H2804 between the limits of 2% and 28, and of water between 15% and 34%. The combined HaP04 and H2804 concentration withln this same area lies between a minimum value of 66% and a maximum value of the same as in the larger composition area.

It will be understood that if plotted on the accompanying .ternary diagram of Figure 1, the bath compositions giving little or no precipitation of nickel lsalts during continued electropolishing will all lie within the` larger area ACDEFGHA if a. proper temperature is selected between 80 and 140 F., and bath compositions within the smaller area BIJKGLMB will give substantially no precipitation of nickel salts if the proper temperature, within the range of from to 125 F. is selected for the composition used.

The relationship between the Acompositions within the larger area in Figure 1 (defined by the lines AC, CD, DE, EF, FG, GH and HA) and the compositions within the smaller area in Figure l (defined by the straight dotted lines BI, IJ', JK, the full line KG and the straight dotted lines GL, LM and MB) is the following. The compositions within the smaller area are yall operative within part or all of the temperature range of I-rom 90 to 125 F. However, other compositions outside the smaller area but inside the larger area may also be operative at a temperature between 90 and 125 F. Note, for instance, that the-area defined in Figure 2 by the lines drawn between points i, 8, 0, 8, 'l and I in the order named includes only compositions operative at 115 F. 'Ihls area in Figure 2 fallspartly outside the smaller area in Figure 1. All compositions operative anywhere within the temper ature range of from 80 to 140 are included within the large area of Figure 1, including those within the smaller area of Figure l.

During the continued operation of a bath composition within the broader or preferred areas shown on the diagram of Fig. l, the dissolved nickel remains at a concentration within th'e range of about 0.5 to 2.5%, calculated as Ni. Since the H2804:H3P04:H20 values shown in the diagram are based on of the bath consisting only of the three mentioned components, the dissolved nickel and hydrochloric acid, or chloride content, alter all components to the same relative amount and to a degree that has nosigniilcant effect on the bath composition and.

'Tanna VI Operating characteristics of nickel electrdpoltshiny bath Y 15% MS04-63% Hmm-22% HzO(0.050.16)% HC! l Refers to total amount ol nickel dissolved during electropolishing al weight per cent ol the bath.

l No precipitation at any tim e. I Refers to total nickel plated out of bath as weight per cent ol the bath.

Tsar.: VII

E tfect of HCI concentration on per cent nickel plated1 at cathode in electropolishina bath containing 12.4% H2504, 56% HsPOl, 25.7% n

H20, 1.2% C1', 2.3% Al l Values are for Bg) cent nickel plated at cathode based on amount d lved at anode for that interval.

l Based on weight ol the bath.

Additions of chlorides may also be used eifectively to cause dissolved nickel to be continuously deposited as metallic nickel at the cathode during electropolishing in the high temperature baths containing additions of trivalent aluminum, or of trivalent aluminum and trivalent chromiuml as has been mentioned previously. Thus, if desired, the advantages of both high temperature operation, say, 180 F. to nearly boiling temperature, and continuous deposition of the dissolved nickel as metallic nickel on the cathode may be obtained. The eil'ect of HC1 concentration on these baths is illustrated by the data in Table VII.`

The baths of the present invention are opera.- tive for the electropolishing of nickel and nickel alloys containing at least 90% nickel together with alloying ingredients in amounts (generally less than 10%) such as will not materially affect the behavior of the nickel for electrolytic treatment purposes. 'I'he principles of the invention include broadly electropolishing nickel in baths containing a minor chloride addition furnished o by any compound selected from the group consisting of hydrochloric acid, metal (including ammonium) chlorides, and chlorinated organic acids.

Figures 2, 3 and 4, as previously noted, show u the effect of operating at different bath temperatures. l

When hydrochloric acid is addedwithin the limits of 0.3 to 1.0% andthe resulting baths are operated at 115 F., no precipitation of nickel 7 li' Sig Hoi ncl HC1 Hoi Hoi solved, 0.25% 0.50% 1.0% 1.5% 2.5% n

polishing and electrodeposition of nickel can be satisfactorily carried out. In the area delineated by the straight lines'joining the points l, Il, II, I2, and l, in the vorder named. a siisht amount of precipitation of nickel salts may occur. but

- such slight precipitation may not be objectionable.

In Figure 2, the preferred bath compositions, with respect to HaPO4- H1SO4-Hz0 when containing from 0.3 to 1.0% HC1 and operated at 115 F., lie within the area delineated by the straight lines joining the points I, I, 0, I3, I4 and vl. in the order named. Within this area. both electropolishing and pickel electrodepositlon can be most satisfactorily performed. The broader bath'composition limits for simultaneous polishing and plating are thoselying within the area defined by the straight lines joining the points I, l, l, Il, Il,

I2. I, I and I in the order named.

'I'he following are the values for the various points indicated by reference numerals on Figure 2:

- Pei-Cent Percent PerCent i no. o. H10

\85 0 FD 73 0 75 l0 62 m 46 32 39 1 3l 39 71 5 77 3 In general, for the operating conditions set forth in commotion with Figure 2, the preferred bath compositions lie within the limits of from to '17% H1PO4, 3 to 20% H1804 andA 15 to 30% H10, and within the area defined by the straight lines I-i, 0-0. O-IS, Il-II and II-l. In the broader bath composition range. the limits are from 31 to 85% HaPO4, 0 to 39% H2804. and 15 to 30% HzO'and lie within the area. defined by the straight lines l-l. l-I, 0--I|. Il-I I, II-I2, I2-l, 0 1, 'I-I.

When hydrochloric acid is added within the limits of 0.3 to 1.0% and the resulting baths are operated at F.. no precipitation of nickel salts occurs if the HJP04H2SO4H1O values arey kept within the area defined on Figure 3 by the straightllnes joining the points Il, 2l, 22, 23, 24, Il, 2l and. Il in the order named. In other u words, this area/represents baths in which simultaneous electropolishlng and electrodeposition of nickel can be satisfactorily carried out. In the v may occur but such slight precipitation may not be objectionable.

In Figure 3, the preferred bath` compositions, with respect to HaPO4-H2SO4-H2O, when containing from 0.3 to 1.0% HCl and operated at 90 F. lie within the area delineated by the straight lines joining the points 22, 23, 24, I9, 21 and 22, in the order named. Within this area, both electropol- .ishing and nickel electrodeposition can be most satisfactorily performed. The broader bath composition limits for simultaneous polishing and plating are those lying within the area defined by the straight lines joining the points I5, 2|, 22, 23, 25, 25, I9, 20 and I5.

The following are the values for the various points indicated by reference numerals on Figure 3:

In general, for the operating conditions set forth in conjunction with Figure 3, the preferred bath compositions lie within the limits of from 38 to 73% H3PO4, 3 to 28% H2SO4, and 24 to 34% H2O, and Within the area defined by the straight lines 22-23, 2li- 24, 2I-|3, |9-21 and 21-22. In the broader bath composition range, the limits are 38 to 85% H3PO4, 0 to 28% H2804 and to 34% H2O and lie within the area dened by the straight lines I5-2 i, 2I-22, 22-23, 23-25, 25-28, 26-|9, i9-20, and 2li-I5.

When hydrochloric acid'is added within the limits of 0.3 and 1.0% and the resulting baths are operated at 135 F. no precipitation of nickel salts occurs if the HaPOi-HzSOi-Hno values are kept within the limits defined on Figure 4 by the straight lines joining the points 28 and 35. In others words, this line 28-35, representing from 74 to 85% H3PO4, 0% H2SO4 and from 15 to 26% H2O, represents baths in which simultaneous electropolishing and electrodeposition of nickel ycan be satisfactorily carried out. In the area delineated by the straight lines joining the points 28, 36, 31, 38, 33, 34, 35 and 28, in the order named, a slight amount of precipitation of nickel salts may occur but such slight precipitation may not be objectionable.

In Figure 4, the preferred bath compositions, with respect to HaPO4H2SO4H2O, when containing from 0.3 to 1.0% HCl and operated at 135 F., lie within the area delineated by the straight lines joining the points 39, 36,31, 38, 33, 34 and 39, in the orde/r named. Within this area, both electropolishing and nickel electrodepition can be most satisfactorily performed. The broader bath composition limits for simultaneous polishing and plating are those lyingwithin the area defined by the straight lines joining the points 28, 36, 3l, 33, 33, 34, 35 and 28.

The following are the values for the various ioints indicated by reference numerals on Figure Icr (lent Per Cent Per Cent I l mt Hai Hisol Hgo 0 l5 50 20 30 n 5 29 74 0 21' 70 l5 l5 50 30 20 40 3() v 3() 75 5 2() 33-34 and .3l-39. In the broader bath com.`

position range, the limits are 40 to 85% H3PO4, 0 to 30% H2804 and 15 to 30% H2O and lle within the area defined by the straight lines 28-36, 36-31, 31-38, 38-33, 33-314, 34-35 and 35-28.

Many details in composition and procedure may be varied within a wide range without departing from the principles of this invention, and it is therefore not our intention to limit the patent granted on this invention otherwise than necessitated by the scope of the appended claims.

What We claim is:

1. The method of electrolytically polishing metal selected from the group consisting of nickel and nickel alloys containing at least nickel, which comprises making the metal the anode in an aqueous bath having a dissolved chloride ion content calculated -as HC1 of from 0.04 to 2.5% by weight of said bath, the remainder of said bath consisting essentially of a composition ly- -ing within the closed area defined on the accompanying diagram by -the solid straight lines AC, CD, DE, EF, FG, GH and HA, passing through said solution while held within the temperature range of from 80 to 140 F. an electrical current of suiicient density and for a sufficient period of time to effect the polishing oi. said metal, and during said electropolishing maintaining said bath at that temperature within said range at which anodically dissolved nickel will be electrodeposited from said bath whereby the tendency of nickel salts to precipitate on continued operation of said bath is reduced.

2. The method of electrolytlcally polishing metal selected from the group consisting of nickel and nickel alloys containing at least 90% nickel, which comprises making the metal the anode in an aqueous bath having a dissolved chloride ion content calculated as lHC1 of froml 0.04 to 2.5% by weight of said bath, the remainder of said bath consisting essentially of a composition lying within the closed area defined on the accompanying diagram by the dotted straight lines BI. IJ, and JK, the solid straight lineKG and the dotted straight lines GL, LM and ,MB, passing through said solution while held within a temperature range of from 90 to 125 F. an electrical current of suiiicient density and for a sufficient period of time tol effect the polishing of said metal, and during said electropolishing maintaining said bath at that temperature within said range at which anodically dissolved nickel will be electrodeposited from said bath whereby the tendency of nickel salts to precipitate on. continued operation of said bath is reduced.

3. For use as 'an aqueous electrolyte in the simultaneous electropolishing of nickel and nickel alloys containing at least 90% nickel and the cathodic electrodeposition of nickel', an aqueous solution having a dissolved chloride ion content calculated as HC1 of from about 0.04 to 2.5%

by weight of said solution and containing disalloys containing at least 90% nickel and the cathodic electrodeposition of nickel, an aqueous solution having a dissolved chloride ion content calculatedas HC1 of from about 0.04 to 2.5% by weight of said solution and containing dissolved nickel in an amount calculated as Ni of from 0.5 to 2.5% by weight of said solution, the remainder of said solution consisting essentially e of a composition lying within the closed area on the accompanying diagram defined by the dotted straight lines BI, IJ and JK, the solid straight line KG, and the dotted straight lines GL, LM and MB. V

5. 'For use as an aqueous electrolyte inthe simultaneous electropolisning of nickel and nickel alloys containing at least 90% nickel and the cathodic electrodeposition of nickel, an aqueous solution having a, dissolved chloride ion content calculated as HC1 of from about 0.04 to 2.5% by weight of said solution and containing up to saturation of dissolved nickeLthe dissolved nickel content calculated as Ni being at least equal' to 0.5% by weight of said solution, the remainder of said solution consisting essentially of a composition lying within the closed area on the accompanying diagram defined by the solid straight lines AC, CD, DE, EF, FG, GH and HA.

6. For use as an aqueous electrolyte in the simultaneous electropolshing of nickel and nickel 16 alloys containing atlleast 90% nickel and the cathodic electrodeposition of` nickel, an aqueous solution having a dissolved chlorideion content calculated'as 4HC1 of from about 0.04 to 2.5% by weight of said solution and containing up to saturation of dissolved nickel, the dissolved nickel content calculated as Ni being atleast equal to 0.5% by weight of said solution. the remainder of said solution Iconsisting essentially of a composition lyingwithin the closed area on the accompanying diagram dened by the dotted straight lines BI, IJ, and JK, the solid straight line'KG lines GL, LM and MB.

CHARLES L. FAUST.,v PAUL D. MILLER.

REFERENCES CITED' .The following references are of record in the 111e of this patent: l

UNITED STATES PATETS and the dotted straight OTHER REFERENCES Modern Electroplating, published in 1942 by The Electrochemical Society, Inc., page 240.

Transactions of the Electrochemical Society, vol. 78 (1940) ,pages 265 through 272. 

